The present invention relates to a method and apparatus for recovering and revegetating soil, particularly along shorelines, where the erosive effects of wind and waves cause enormous ecological damage and economic loss. The invention is also suitable for use in a variety of other terrestrial applications, such as on slopes, in ditches, and in natural drainage areas subject to erosion processes.
Various attempts have been made to control erosion, and at the same time, to encourage plant growth. For example, in U.S. Pat. Nos. 4,353,946 and 4,283,445, so called "mulch blankets" are disclosed which are fairly complex structures containing fibrous materials, held together by biodegradable binders. These structures are typically expensive to manufacture, and difficult to handle by reason of their great weight.
Attempts have also been made to fix sandy soil or other substrates by spraying vinyl emulsions, petroleum mulches, etc. to form a crust on the soil. The crusts, however, are often destroyed by wind and/or other physical disturbance.
In U.S. Pat. No. 4,158,932, a non-woven textile filament network is positioned over sandy terrain, and is said to prevent erosion while allowing seeds to germinate.
These approaches, however, are not completely satisfactory and are not particularly suited for use in coastal areas subjected to moderate wave energy.
Typically, erosion control in coastal zones involves massive planting of shrubs and/or grasses. While this approach is oftentimes successful in low energy areas, i.e., areas with little or no wave action, in moderate and high energy wave areas the shrubs and grasses are often washed away, particularly in the time period immediately after planting and before the root systems of the plants have had a chance to develop and anchor plants to the substrate.
In high energy wave areas, structural barriers such as wooden bulkheads and offshore breakwater are often employed with varying degrees of success.
There remains a real need for an effective system of erosion prevention and revegetation in low to moderate wave energy areas, and in other terrestrial applications where conventional planting techniques have not been successful, and where the more extreme structural approach is undesirable for aesthetic and/or economic reasons.
This invention provides a simple and inexpensive, yet extremely effective solution to the problem of erosion and plant growth areas subject to erosion and particularly in coastal zones exposed to moderate to low wave energy. According to this invention, a lightweight, flexible and biodegradable mulching material is employed which protects newly installed plants from washout; encourages sand aggregation from sediment suspended in the water; and stabilizes the shoreline or other substrate. These functions are accomplished by providing the mulching material in sheet form, with upper and lower, three dimensional surface configurations for dissipation of energy as waves (or drain water) flow over, through and around the surface contours of the material. These same contours also serve as traps for accumulating sand, and therefore preventing washout.
More specifically, the mulching material in accordance with this invention is constructed of lightweight material, preferably cardboard, rolled or stamped to include three-dimensional contours on its upper and lower surfaces in a manner similar to conventional egg cartons, and as described in more detail below.
The material is also preferably provided with suitable soil and plant nutrients which are released as the sheet degrades over time. In addition, the sheet material is also provided with a plurality of apertures to facilitate installation of plants such as salt marsh hay, smooth cordgrass or other suitable grasses, plants, etc. in the area to be recovered. It will be appreciated that the number and size of the apertures will depend on the plant density requirements, initial and mature size of the plants, and so on.
The biodegradable sheet is further provided with a hydrophobic surface coating, such as a paraffin composition, which will delay biodegradation of the material to insure plant root development.
The material may be manufactured in any number of standard or custom sizes. For example, four by eight foot sheets provide a convenient and easily workable size for large areas. Other sizes may be produced, depending on the terrain, the area to be covered, etc.
The biodegradable mulching material according to this invention is thus seen to have the following advantages:
(1) It is flexible enough to follow the natural contours of the shoreline or other terrain;
(2) It stabilizes existing shoreline or other terrain from further erosion;
(3) It can be used to accommodate a wide range of vegetation;
(4) It provides protected areas for rhizome development by allowing sunlight through small openings in the sheet surrounding the plants;
(5) It provides a predetermined density format for placement of plants;
(6) It can be produced in a variety of sizes and shapes;
(7) It can be dyed to the desired shade so as to be virtually invisible;
(8) It is inexpensive to produce and easy to install; and
(9) It is extremely light, easy to work with, store, and transport.
Additional objects, advantages and details with respect to the invention are made apparent from the detailed description taken in conjunction with the accompanying drawings.